The present invention relates to turbo-machinery and, more particularly, to an instrumentation light probe holder for use in observing and measuring operating characteristics of rotating blades or airfoils of a gas turbine engine during engine operation.
Gas turbine engines include a multiplicity of airfoils or blades arranged in rows extending radially from an axially aligned shaft. The rows of blades are rotatable in response to the force of high pressure gases flowing axially through the engine. Because of the complex shape of the blades and the forces and stresses exerted on the blades during engine operation, it is desirable to observe the blades during engine operation for the purposes of measuring operating characteristics of the blade, such as optical blade vibration, axial displacement of the blade, blade untwist and the like.
A currently used fiber optic light probe has one end which is threaded to permit screwing into a matingly threaded opening through a casing of a gas turbine engine to provide illumination of an end-on view of the engine's passing blade tips and to also collect light reflected from the passing blade tips. These light probes are typically about 20 feet long from the end screwed into the engine casing to an opposite end which is bifurcated to allow a portion of the optical fibers to be connected to a light source and the remaining optical fibers to be connected to a photodetector for the purpose of measuring blade vibration, blade untwist, axial displacement or other blade operating parameters or characteristics. A lock nut disposed around the threaded portion of the light probe may be tightened against the casing to secure the one end of the light probe in the casing.
One disadvantage of this probe is that the entire 20 foot length of the probe must be rotated, preferably while the probe is laid out substantially in a straight line, through a number of turns necessary to install or remove the probe, or to move the probe to a new observation location. For example, if the probe end is threaded at #10-32 threads per inch (TPI), 32 rotations would be required to insert or remove the probe from a 1 inch thick casing. Additionally, the probe may be routed around and over the engine and tie wrapped at various intervals to secure it. These tie wraps would, therefore, also have to be removed if the probe is removed or moved to a new location.
Another disadvantage is that the installation of each new probe or relocation of a probe requires that the probe be inserted and set to a proper "set-back" position relative to the passing blade tips to prevent the probe from interfering with the rotating blades which could potentially damage the probe and/or the blades.
A further disadvantage is that these probes cannot be quickly and easily removed for cleaning or as previously discussed relocated to another observation location.
It is, accordingly, a primary object of the present invention to provide a novel instrumentation light probe holder which is not subject to the foregoing disadvantages.
It is another object of the present invention to provide a novel light probe holder which does not require resetting of the set-back distance from the blade each time a new light probe is installed or the probe is moved to a new location.
It is a further object of the present invention to provide a novel light probe holder which permits faster and easier relocation of light probes or cleaning of the light probes without the need for test personnel having to climb into the bell mouth of the engine.
These and other objects of the invention, together with features and advantages thereof, will become apparent from the following detailed specification when read with the accompanying drawings in which like reference numerals refer to like elements.